After six years in office, Armenia’s Prime Minister Tigran Sarkisian has stepped down unexpectedly for reasons that were not immediately clear.

The ruling Republican Party of Armenia (HHK) said that Sarkisian announced his resignation at a meeting of its governing body chaired by President Serzh Sarkisian.

“The prime minister said that it is his personal decision,” HHK spokesman Eduard Sharmazanov told a news conference after the meeting. “He thanked all of his colleagues, all government members, and all HHK representatives for the joint work and asked us to grant his request.”

The premier confirmed his resignation on his Facebook page. He too gave no reasons for the move. “I wish the new government productive work for the good of the country,” he wrote.

According to Sharmazanov, Sarkisian first tendered his resignation a month ago but was asked by the president to continue performing his duties until a Constitutional Court ruling on a controversial pension reform implemented by the government.

The ruling party representative refused to be drawn on reasons for the move. He insisted only that it has nothing to do with a vote of no confidence in Sarkisian’s cabinet which Armenia’s four main opposition parties planned to propose in the parliament on April 28.

Under the Armenian Constitution, all government ministers must also step down if the prime minister is dismissed or decides to quit.

Sharmazanov said that the HHK leadership did not discuss any candidacies for the post of prime minister. “The appointment of the government and the prime minister is the prerogative of the president of the republic and the [HHK-led] parliamentary majority,” he said. “In accordance with the constitution, the prime minister will discuss the composition of the government with the majority and all factions of the National Assembly.”

Tigran Sarkisian, 54, was appointed prime minister shortly after Serzh Sarkisian took over as Armenia’s president in April 2008. He was previously the governor of the country’s central bank.